This invention relates to multiple coated articles exhibiting selective reflectance and transmittance of radiation over an extended spectral range, and more particularly relates to visibly transparent articles having such selective reflectance. In another embodiment, this invention relates to an electroless coating method for producing such articles.
In the past, multiple layer coatings have been employed which provide particular reflectance and transmittance characteristics for the composite film. Exemplary of this prior art is the basic work of G. L. Dimmick, for example, U.S. Pat. Nos. 2,379,790, 2,412,496, 2,422,954 and 2,624,238. Particular coating materials employed in the prior art and disclosed in these references are a relatively high-index refraction material selected from lead molybdate, lead tungstate, lead chromate, titanium dioxide, magnesium oxide, lead oxide, bismuth oxide and preferably zinc sulfide and a low index of refraction material selected from magnesium fluoride, calcium fluoride, calcium silicate, lithium fluoride, aluminum fluoride, aluminum oxide and preferably thorium oxyfluoride (cryolite). In the application of such layers according to the prior art, it is necessary to employ vaporization techniques or other techniques requiring a vacuum. The techniques of this prior art are not particularly effective for the production of coatings on large substrates, such as those intended for viewing closures in buildings or vehicles.
Other workers in the art have modified the basic concepts of Dimmick to include metal films or foil and semimetal films in combination with the particular high index of refraction materials taught by Dimmick. Exemplary of disclosures relating to these modifications is U.S. Pat. No. 3,516,720 which discloses the use of two metal films in combination with layers of high index of refraction material according to Dimmick where the particular metal films are a nickel film and a gold or copper film separated by a layer of zinc sulfide. As with the articles and techniques of Dimmick, the preparation of these combination films or coatings are practically limited to their preparation on small substrates such as the sunglasses which are prepared according to this reference.
In the preparation of transparent, reflective metallic films on large substrates, there has been a large body of teaching relating to preparation of such coatings by electroless techniques which have developed from the art of the preparation of mirrors. Exemplary of such teachings are U.S. Pat. No. 3,457,138 to Richard G. Miller for the preparation of copper films and U.S. Pat. Nos. 3,672,939, 3,674,517 and 3,723,158 for the preparation of iron, cobalt or nickel films.
It has also been known in the past to prepare copper coatings on large substrates with the outer or exposed portion of the film oxidized so that a composite copper oxide/copper film results; see U.S. Pat. No. 3,537,944. The copper oxide coatings so produced are not found to provide for a variety of products having different characteristics which may be modified at will by simple control of the process for forming such coatings. Such coatings do not appear to have a sharp plane of demarcation between the copper oxide and the copper, but instead appear to have a gradual change from copper oxide to copper through their thickness and are not found adaptable for providing specific interference colors.